Backpack



FIG. 1 is a front-left perspective view of a backpack, showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a back view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines in the figures are for the purpose of illustrating portions of a backpack that form no part of the claim. 

CLAIM The ornamental design for a backpack, as shown and described. 